Pilot responsive safety control for liquid fuel burners



Sept. 9, 1947. UB 2,427,178

PILOT RESPONSIVE SAFETY CONTROL FOR LIQUID FUEL BURNER-S Filed DEC. 2, 1943 7 INVENTOR 3M 6; W

BY M 4 1.1 ATTORNEY Patented Sept. 9, 1947 I UNITED STATES PATENT OFFICE PILOT RESPONSIVE SAFETY CONTROL FOR LIQUID FUEL BUBNEBS Fred B. Aubert, Grease Polnte, Mich. Application December 2, 194:, Serial no; 512,551.

10 Claim.

An object of the invention is to provide such an apparatus in which the sequence of starting and of running operations is automatically supervised.

Another object is to render the starting of the burner dependent upon proper viscosity of the liquid fuel.

Another object is to provide means for checking the operation of the burner igniting means preliminary to the supplying of fuel to the main burner.

The invention consist in the cooperative relation of the control devices comprising the system or apparatus and in the devices themselves. the novelty of which will be more fully described hereinafter and will be particularly pointed out and distinctly claimed. g

In the accompanying drawing to be taken as a part of this specification, there is fully and clearly illustrated a preferred embodiment of the invention, in which drawing the flgure is a diegrammatic view showing a heating apparatus with it interrelated control devices and their interconnecting electrical circuits.

Referring to the drawing by characters of reference, I designates generally a heating-apparatus such as a boiler or furnace for generating power, although it will be apparent that theinstallation may serve also or solely for space heating. The apparatus I has a combustion chamber 2 underlying or in heat exchange relation with the usual boiler water space or other chamber for containing a medium to be heated. The combustion chamber 2 is equipped with a fluid fuel burner 3 such as an oil burner having a combustion air supplying conduit or duct 4 fed with air under pressure from a blower 5 driven by an electric motor 6. Fuel such as oil, in combustible proportions with the air supplied. by the blower I, is supplied to the chamber 2 through a fuel supply pipe or conduit I having a spraying nozzle 8 discharging into the chamber 2, the pipe 1 having intercalated therein an electrically operated shut off valve 9 with an electromagnetic operating coil III.. The fuel is fed through the pipe 1 from' a fuel supply source or tank (not shown) by a pressure pump I I driven by the motor fl'through any suitable gearing or drive mechanism. Also in the length of the pipe I- there is a fuel heating section or portion I2 which is positioned on the inlet side, but may be on the outlet side, of the 2 pump II. The pipe section I2 has an electric heating means II which may be in the form of an electric resistance coil, preferably in direct heat exchange relation with the oil in the pipe I and which functions to increase the oil temperature and decrease the viscosity of the oil for it proper feeding to and through the nozzle 8. The combustible mixture of air and fuel discharged into the combustion chamber 2 is ignited by the flame from a gas or fluid fuel pilot burner I 4 having the usual combustion air supply. Fuel is fed to the burner I 4 through a pipe I! having intercalated therein a shut off valve II which is elecr trically operated and controlled by an electromagnetic coil II. The gas mixture discharging from the pilot burner I4 is ignited by spark electrodes I8 supplied from the secondary coil of an ignition transformer I! which has its primary coil 20 connected by lead wires 2|, 22 to a source of current supply. Cooperable with the pilot burner there is a. photo-electric cell or tube 22 contained in a box or casing having a light conducting sight tube or conduit 24 directed toward the pilot flame, the cell 23 being rendered conductive upon the impingement of light thereon resulting from the occurrence of flame at the pilot burner. The sight tube 24 provides a shield, protecting the pilot burner cell 23 against ,response to the light of the main burner flame. Cooperable with the flame from the main burner there is a photo-electric cell or tube 25 contained within a box or casing having a light conducting sight tube or conduit 26 directed toward the main burner flame, the cell 25 being rendered conductive upon the impingement of light thereon resulting from the occurrence of flame at the main burner. The main burner cell 25 is protected and shielded from response to the light of the pilot burner flame by the sight tube 2.

The control system and heating apparatus is supplied with current from any suitable commercial or high voltage source through lead or service line wires 21, 28. The wire 2l is connected to the manually operated contact carrying switch arm-.29 of a main control switch 30 which is manually movable into and out of electrical contacting engagement with a fixed contact 3| of switch ill by means of a control handle or knob 32. Cooperable with theswitch arm 29 there is an electromagnet or holding coil 33 which is of a strength only sufllcient to hold the switch' 30 closed against the force of a switch opening spring 34 acting on the arm 29. The flxed switch contact ll is connected by a lead wire 35 to one terminal of the motor 6, the other motor termiml being connected by a lead wire 88 to the service line wire 28. Connected to the motor lead wire 35 there is a lead'wire 31 which connects to one terminal of the primary coil 38 of the main control system step down transformer 39 having a secondary coil 45. The other terminal of the primary coil 38 is connected by a lead wire 4| to the service line wire 28. Extending from the lead wire 31 there is a lead wire 42 which connects to one end or terminal of the heating means or resistance coil i3 which has its other end or terminal connected by a lead wire 43 to the service line wire 28.

The coil 38 of the main switch 88 is controlled by a pilot flame responsive electron tube relay switch 44 having a relay coil 45 and is also controlled by a safety relay switch 45. The relay coil 45 controls a normally closed single throw switch 41 having a contact carrying arm 48 and also controls a double throw switch 49 having a contact carrying arm 58. The switch arms 48, 50 of which one or both may cooperate with the coil 45 as armatures, are movable in unison and are preferably mechanically connected together by a link to assure simultaneous movement. The contact member of switch arm 48 is normally in engagement with its fixed switch contact The double throw switch arm 58 has one of its contacts normally in engagement with avflxed switch contact 52 when in coil deenergized position and has its other contact normally open and operable to engage a fixed switch contact 58 upon energization of coil 45. The safety switch 45 has a relay coil 54 controlling a single throw switch '55 having a contact carrying switch arm 58 engaging its fixed switch contact 51, such that the switch 55 is normally closed when the coil 54 is deenergized. The relay switch 45 also includes a holding switch 58 with a contact carrying switch arm 59 cooperable with its fixed switch contact 5|);the switch 58 being normally open when the coil 5a is deenerglzed. The arms 55 and 59 of which one or both may cooperate with the coil 54 as armatures, are movable in unison and are preferably mechanically connected together as by a link to assure simultaneous movement. The control of the main switch holding coil 33 by switch 55 of the safety switch" and by the double throw switch 49 of the electron tube relay switch 44 upon energization of transformer secondary coil 48 is through the following circuit: From one terminal of the transformer coil 40 via a lead wire 6| to the switch contact arm 58 of the double throw switch 49, through switch contact 52 and lead wire 52 to the fixed contact 51 of safety switch 55, thence through switch arm 58 and lead wire 53 to one terminal of the coil 33 and from the other terminal of coil 33 via lead wire 54 back to the other terminal of the transformer-coil 48.

The oil delivery pipe section or portion |2 has in intimate heat exchange relation therewith a temperature responsive switch 55 which may comprise a bimetal actuator 58 in physical contact with the section l2 or with the oil therein and operable to move a contact carrying switch arm 81 into and out of engagement with a. fixed switch contact 88. The temperature switch 55, when the oil gets up to temperature after closure of switch 39, controls the starting or running of a timer means 59 such as an electrically driven timing motor which drives a shaft 18 having fixed thereon an ignition controlling cam 1|, a pilotburner controlling cam 12 and a main burner controlling cam 13, the cams being rotated in a clockwise direction facing the drawing as shown by the arrows. The cam 18 has a cam lobe 14 angularly spaced from its follower member 15 so that a lapse of say twenty (20) seconds following energization of motor 69 occurs before lobe 14 actuates follower member 15. The follower member 15 of electric insulating material operates a normally open single throw switch 18 and a double throw switch 11. The switch 18 has a contact carrying resilient switch arm 18 mounted on a support 19 and connected to the follower member 15. The contact member of arm 18 is cooperable with a resiliently mounted fixed contact 89 carried by a switch blade secured to the support 19. The switch 11 has a contact carrying resilient arm 8| connected to the follower member 15 and mounted on the support 18, one contact member of arm 8| normally being in engagement and cooperable with a resiliently mounted fixed contact 82 carried by a switch blade mounted on the support 18. The other contact member of arm 8| is normally open and engageable with a resiliently mounted fixed contact 88, carried by a switch blade mounted on the support 19. The switches 18 and 11 and the contact supporting arms and blades thereof are electrically insulated from each other u by a mounting rod and spacer sleeves of insulating material. The follower member 15 is mechanically connected as by a pin and slot engagement to a pivoted arma ture 84 cooperable with a holding magnet 85. When the follower member 15 is moved by lobe 14 and closes the switch 18 and the arm 8| against contact 83, the armature 84 will be positioned in magnetic holding relation to the electromagnet 85. It is to be noted that the magnet 85 does not have suillcient strength to close the switch 18 and the switch contact 83, the cam lobe 14 being required to perform this operation. Upon closure of the temperature switch 85, the timing motor 59 is energized by the following circuit: From switch arm 51 through lead wire 85 to the switch arm 8| of the double throw switch 11, thence from closed contact 82 through lead wire 81 to the switch arm 48 of the single throw safety switch 41 ofthe tube relay switch 44, thence via switch contact 5| and lead wires 88, 89 and 88 in series to one terminal of the motor 59 and from the other motor terminal via lead wire 8| to the lead wire 54 which is connected to the transformer secondary 40 and thence from the transformer lead wire 8| through lead wire 92 to the oil temperature switch fixed contact 88. The timing motor lead wires 98 and 9| are connected respectively to and to feed the ignition transformer lead wires 2|, 22 so that the ignition transformer I9 is energized upon closure of the temperature switch 85. The closure of switch 85 also energizes the electromagnet 93 to hold in cam operated position the follower member 85 of electric insulating material which is cooperable with a cam lobe 95 of the timing motor ignition 1 pilot controlling cam 12, the magnet circuit being as follows: From lead wire 88 of switch 41 to lead wire 81 connected to one terminal of the coil of magnet 93 and from the other magnet coil terminal via lead wire 98 to lead wire 84 connected to secondary coil 40. The electromagnet 98 has insufficient strength to move its pivotally supported armature 99 from inactive position, the armature being operatively connected as by a pin and slot engagement with the follower member 85.

Substantially instantly upon starting of the timer motor 59 and of initial rotation of the cam 1|, which is preferably a circular disc having a low point formed'by an edge recess I00, the cam follower member IIII is forced or cammed out of the recess I into which the follower member IOI drops or moves upon a complete rotation of cycle of operation of the shaft I0. The follower member IOI operatively engages a resilient switch arm I02 mounted on a support member or structure III of electric insulating material. The arm I02 operates the normally .opene'd switches I04, I06 having resiliently mounted fixed contacts I06, I" respectively, the contact I0I being mounted by its resilient blade, from the supporting member I03. circuit for the main switch holding coil 33 as follows: From transformer lead wire 6| to lead wire 92, thence via lead wire I00, to switch arm I02 and from closed contact I06 via lead wire I09 to lead wire 63, connected to the coil 33 and thence back to the transformer via lead wire 64. Closure of switch I establishes a holding circuit for the timing motor 69 from the transformer lead wire I08 and switch arm I02 to the closed contact I0! and lead wire IIO to the motor lead wire 90. Since the lead wire IIO also connects to the lead wire 89 which is connected to lead wire 91, the holding magnet 93 of cam fol- Closure of switch I04 establishes a. holding lower member 95 will be held energized upon opening of the pilot tube relay switch 41 as long as switch I05 remains closed. The switch I05,.

since it feeds lead wire 90, also establishes a parallel circuit for the ignition transformer I9 so that the ignition transformer will remain energized subsequent to the opening of the electron tube relay switch 41 and until the follower member IOI moves into its cam recess I00.

Subsequent to closure of switches I04 and I05, the cam I2 will rotate the cam lobe 96 into engagement with the follower member 95, there being preferably a lapse of say fifteen (15) seconds before the armature 99 is moved into holding relation with its coil 93 and the resilient contact carrying switch arm III, mechanically connected to the follower member 95, is moved into engagement with its resiliently mounted fixed contact H2. The arm III and contact II2 comprise a pilot burner controlling switch H3 and are mounted on a supporting member or structure II4 of electric insulating material. Closure of switch II3 establishes a circuit for the gas valve coil I! that feeds from the secondary coil lead wire BI through lead wire I I5 to switch contact H2 and thence via switch arm III and lead wire II6 to one terminal of the coil I1 and from the other coil terminal via lead wire II! to the lead wires 98 and 64 connected to the transformer secondary coil 40. Opening of the valve I6 by energization of coil I! will supply a combustible mixture of gas and air to the pilot burner I4 for ignition by the spark at the energized electrodes I8. The pilot flame will render the photo-cell 23 conducting and since the photo-cell 23 connects the control grid II8 of the electron tube II9 to ground via lead wires I20 and I'll, the tube II9 will be rendered conducting'and current will flow through the relay coil 45 of the tube relay switch 44. Energization of the coil'45 will operate the switch arms 48 and 50 to open the switch 41 and to break circuit at switch 49 with contact 52 and to make contact with contact 53. The opening of switch 41 has no effect upon th circuits initially closed thereby, as such circuits as above noted have been completed through additional switches. The opening of the switch 49 at contact 52 also has no effect upon the holding coil 33, as the holding coil circuit is also completed through the. timer motor operated switch I04 as above described. Closure of contact 53 of double throw switch 49 establishes a preparatory circuit for the main burner and a holding circuit, hereinafter described, for the main switch holding coil 33.

The electron tube II9 forms part of an electrical network which is energized by a transformer I22 having a primary coil I23 connected by lead wires I24, I25 to the lead wires 31 and M respectively which are connected to the main service wires 21, 28 respectively, The tube II9 has an anode I26 connected by a lead wire I21 to one terminal of the coi1 45, the other terminal of this coil being connected by a leadwire I28 to a transformer secondary coil I29 of the transformer I22. From'an intermediate tap I30 of coil I29, to provide a plate voltage of say 142 v., there is a lead wire I3I connected to ground as at I32 and to the tube cathode I33 which is heated by a filament I34 energized at say 6 v. by the end turns or portion I35 of the coil I29. The extent to which the grid II8 must become positive is-controlled by a shield grid I36 which is connected to the cathode filament return lead wire I36 by a conductor I31 having a resistor I38 therein. The photo-cell lead wire I20 is connected by a lead wire I39 through a variable condenser I40 to the negative terminal of a secondary coil I4I of the transformer I22, the coil I4I having its positive terminal connected'to ground as at I42. In the photo-cell lead wire I20 intermediate the control grid II8 and the lead wire I39 there is a resistor I43. The photo-cell lead wire I20 is also connected between the resistor I43 and the photo-cell by a lead wire I44 to balancing condensers I45, I46, which are connected respectively to the high voltage lead wires I24 and I25.

Upon the lapse of the above mentioned twenty (20) seconds interval which has brought the cam lobe I4. into operative engagement with the follower .member I5, the follower member I5 will be actuated to close the fuel supply controlling switch I6 and to operate the double throw switch TI to break circuit at contact 82 and to make circuit at contact 83 and also to move armature 84 into holding relation with the holding coil 85. Closure of switch I6 will energize the operating coil I0 of fuel valve 9 to open this valve for supply of fuel under pressure from the pump II to I the burner nozzle 8, the circuit being as follows: From the now closed tube relay contact '53 via lead wire I4! to the cam switch contact 80, thence through switch arm I8 andlead wire I48 to one terminal of valve coil I0 and from the other valve coil terminal via lead wire I49 to lead wire I IT.

The closure of the pilot flame switch contact 53 also completes a holding circuit for the main switch holding coil 33, as follows: From switch arm 50 to its closed contact 53, thence via lead wire I41 and lead wire I4! to the lead Wire I09 which is connected to lead wire 63 leading to the coil 33 as above described.

The combustible mixture of fuel and air discharging from the main burner into the combustion chamber 2 will be ignited by the flame from the pilot burner I4. Instantl upon the occurrence of the main burner flame, the photo-electric cell 25 will 'be rendered conducting, thereby rendering the electron tube I50 conducting by the connection of the control grid I5I to ground through lead wire I52 leading to the cell 25 which is connected to ground, as at I53. Energization of the tube I50 will establish the circuit for a tube relay switch I54 having a magnetic relay coil I55 with one terminal connected by lead wire I56 to the electron tube anode I51. The other terminal of coil I52 is connected by lead wire I58 to one end of a secondary coil I59 of the electron tube network controlling transformer I60, the coil I59 preferably being tapped to provide a voltage of say 142 v. on the relay coil I55. The transformer I60 has a primary coil I61 connected in parallel with the transformer primary coil I23 and across the lead wires I24, I25. This electron tube I50 forms part of an electrical network substantially identical with the network of the tube H9, and, therefore, a detailed description is believed unnecessary, It may be noted, however, that the tube I50 has a shield grid I62, cathode I63 and heater filament I64. The relay switch I54 has switches I65, I66 with switch arms I61, I68 respectively, which are movable in unison and preferably mechanically connected together as by a link for simultaneous movement. The switches I65, I66 are normally open, the switch arm I61 being cooperable with a fixed contact I69 and the switch arm I68 being cooperable with a fixed contact I10. Upon. closure of the switch I66 a circuit will be completed from the thermostatic switch 65 through the now closed contact 83 of the cam operated switch 11, the circuit being from contact 83 via lead wire I1I to the fixed contact I 10 of switch I66 and through switch arm I68 and lead wire I12 to one terminal of the holding magnet 85 and from the other terminal of the magnet 85 through lead wire I13 to the lead wires 98 and 64 to the transformer secondary coil 40. The closure of switch I65 by coil I55 will establish a circuit from lead wire I1I through lead wire I14 to fixed contact I69 and thence through switch arm I61 and lead wire I15 to lead wire I41 at lead wire I41 so that a circuit in shunt or parallel with the pilot flame switch contact 53 is established for the main switch holding coil 33; The lead wire IN is also connected by a lead wire I16 to one terminal of the safety relay switch coil 54 so that when switch 55 isopened, the starting circuit for the coil 33 will be broken. The initial energizing circuit for coil 54 is therefore from transformer secondary 40 via lead wires 6| and 92 to the open switch 65. When the switch 65 is closed by desired oil temperature, the circuit continues thence through lead wires 86 to switch blade 8| of cam switch 11, to contact 83 and via lead wires HI and I 16 to one terminal of relay coil 54. The other terminal of coil 54 is connected by lead wire I11 to the lead wire II1 which is connected through the wires 96 and 64 to the other end of the transformer secondary coil 4|). The lead wire I16 is also fed from a lead wire I18 connected to the fixed switch contact 60 of the holding switch 56 so that upon closure of switch 58 it will maintain its own holding circuit for coil 54 until transformer coil 40 is deenergized, the holding circuit being as follows: From lead wire 86 to a lead wire I19 connected to the switch arm 59, thence through closed contact 60 and lead wires I 18, I16 to the holding coil 54, and therefrom via lead wire I11 as above recited.

The operation of the controlling system and apparatus is as followsqWhen heat is desired, the manually operated, magnetically held, main switch 30 is closed, which closes the following, heretofore described, high voltage circuits from line wires 21, 28, namely, the circuit to the motor 6 for driving the blower and pump II the circult to the oil heating resistor or element I3, and

the circuit to the primary coil 38 of the control system transformer 39. Energization or the transformer 39 energizes th holding coil 33 of the main switch 30 through the closed contacts of the double throw switch 49 of the pilot photocell relay 44 and through the closed contacts 01 switch 55 of the safety relay 46. This circuit for coil 33 is as follows: From the transformer secondary coil 40 through wire' 6| to switch arm 50 and closed contact 52 of switch 49, lead wire 62 to closed contact 51 and arm 56 of switch 55, lead wire 63 to coil 33 and from coil 33 through wire 64 back to transformer coil 40, When the oil, heated by the energized element I3, reaches the desired degree of temperature for proper viscosity at which it will spray readily from nozzle 8 and mix with the air supplied from conduit 4, the bimetal element 66 closes its oil temperature switch 65 to close the circuit of the timer motor 69 through the closed single throw switch 41 of the pilot photo-cell relay 44 and through the closed double throw timer motor cam switch 11, the circuit being as follows: From transformer coil 40 through lead wires 6| and 92 to closed contact 68 and arm 61 of temperature switch 65, thence through wire 66 to cam operated arm 6| and closed contact 62, through lead wire 81 to arm 48 of switch 41 and its closed contact 5|, thence through wires 88, 89 and 90 to the timer motor 69 and from motor 69 through wires 9| and 64 back to the transformer coil 40. The closure of temperature switch 65 also energized the pilot ignition transformer. I9 which has its primary coil 20 in parallel or shunt with the motor 69, as above noted. The closure of the temperature switch 65 also closed the circuit of the gas valve cam switch holding coil 93 through the pilot tube relay switch 41 preparatory to operation of the pilot gas valve switch 3 by its timing motor cam 12, the circuit being as above described. Initial operation of the timer motor 69 acts through the timer motor controlling cam 1| to close the holding switch I05 which, as above described, completes a holdin circuit for the timer motor and also establishes in parallel with the pilot flame relay switch 41, a circuit for the primary coil 20 of the pilot ignition transformer I9. Switch I05 also establishes a circuit for the holding coil 93 of the cam operated pilot valve switch II3, which circuit is in parallel with the circuit through switch 41. Substantially simultaneousl with its closure of switch I05, the cam 1| also closes the holding switch I04 in parallel circuit with the pilot burner electron tube relay switch 49 for the main relay coil 33, the circuit being as above described. Continued operation of the timing motor 69 for a period of say 15 seconds rotates cam 12 to close the cam operated gas valve switch I I3 which is thereupon held in closed position by the magnet 93, thereby completing the described circuit leading directly from the main transformer secondary coil 40 via wires 6| and M5 to and through switch H3 to the gas valve coil I1 to open the gas valve I6, the circuit thence leading directly back via lead wires H1, 98 and 64 to the transformer coil 40. If the gas mixture thus supplied to the pilot I4 is ignited by the ignition spark electrodes I6, the electron tube II9 controlled by the pilot photocell 23, responding to pilot flame, becomes conductive so that current flow therethrough energizes its tube relay coil 45 which breaks circuit at the single throw starting switch 41 for the timing motor 69 which, however, continues in operation due to its shunt circuit through its holding switch I05. double throw switch 49 to break the initial circuit for the main switch holding coil 33 which, however, is maintained energized by prior closure of its shunt circuit by operation of the holding switch I04 by the timing motor cam 1 I. Operation of the double throw switch 49 by coil 45 closes a circuit which branches, one branch leading from contact 53 via wires I41, I41, I09 and 63 to the main holding coil 33, and another branch closing from contact 53 a preparatory circuit I41, 80 to the open cam switch 16 for lthe oil valve 0. Continued operation of the timing motor for a period of say five seconds brings the oil valve switch operating cam 14 into operative position to move its follower member 15 to close its oil valve switch 16 which completes a circuit from the above mentioned branch circuit I41, 80 to the oil valve coil I via lead wire I48 and thence back via lead wires I49, H1, 98 and '64 to the transformer coil 40. Simultaneously with closure of switch 16, the follower mem- The coil "also operates the her 15 breaks the timin motor starting circuit at switch contact 82, makes a controlling circuit at contact 83 and moves the armature 84 into holding relation with magnet 85. The fuel pump was started in operation simultaneously with the blower and since the heating element I3 has now brought the fuel to proper viscosity, oil will be discharged, the valve 9 being open, with the air into the combustion chamber 2 to provide a combustible mixture to be ignited by the gas. pilot flame at burner I4. The occurrenc of flame at the main burner is recognized by photocell which becomes conducting, thereby renderin the electron tube I50 conducting-to energize tube relay coil I55, which closes switches I65 and I66 which are supplied solely from contact 83 of cam switch 11, The main burner flame must occur during the one or two second interval while cam 14 is hOlding switch 11 closed at contact 83, because it is through this switch and the flame relay switch I66 in series that the holding coil 85 is energized. If flame does not occur at the main burner substantially instantaneously that the switch 16 is closed or before the oil valve cam 14 moves away from switch closing position, the main burner electron tub I50 will be blocked by the photocell 25, so that the tube relay I54 will be deenergized and accordingly, the oil valve switch 16 and the double throw switches 11, 83 will snap to open positions. Closure of flame relay switch I65 establishes a holdin circuit for the main switch coil 33, so that the system will be maintained in operation when cam 1I releases switch I04. Switch I65 also establishes a circuit in parallel with the pilottube relay switch contact 53, so that when cam 1I releases switch I85 to deenergize holding coil 93 forthe pilot gas valve switch II 3, a circuit for the oil valve I0 will be maintained closed. The main burner will now continue in operation until main switch is manually opened, which will deenergize 10 ing coil 33, since its starting circuit through the safety relay switch 55 is open due to its coil 54 having been maintained energized by its holding switch 58 from temperature switch 65, even for igniting said main burner, electrically operable means to supply liquid fuel to said main burner and having a controlling circuit, at least two switches in said circuit, means operable to close one of said switches upon occurrence of flame at said pilot burner, timing means to close for a short period the other ofsaid switches to complete said controlling circuit, means to heat the liquid fuel to be supplied to said main burner, means responsive to the temperature of the heated fuel and operable to start operation of said timing means, electronic control means instantly responsive to flame at said main burner and operable to hold said other switch closed, and a switch in parallel circuit with said one switch and closed by said electronic control means in response to flame at said main burner.

2. A fluid fuel burner controlling apparatus comprising a main burner, means to supply fuel to said main burner and having a controlling circuit, two switches in series in said circuit, a pilot burner for igniting the fuel supplied to said main burner, means to supply fuel to said pilot burner,

electrically controlled ignition means for the fuel supplied to said pilot burner, timing means, means to energize said timing means and said electrically controlled ignition means, pilot burner controllingmeans operable by said timing means subsequent to operation ofsaid ignition means to render said pilot burner supplying means effective, means instantly closing one of said switches upon occurrence of flame at said pilot burner, and means controlled by said timing means subsequent to separation of said pilot burner controlling means and operable to close the other of said switches to render said main burner fuel supplying means effective.

3. A fluid fuel burner controlling apparatus comprising a main burner, means to supply fuel to said main burner, a pilot burner for igniting the fuel supplied to said main burner, means to supply fuel to said pilot burner, electrically controlled ignition means for the fuel supplied to said transformer 39 thus deenergizing holding magnet 85 so that the oil valve switch 16 will snap to open position, thereby cutting off the supply of fuel to the nozzle 8. If, during operation of the main burner there is a flame failure or if relay coil I55 is deenergized for an other reason, such as for example a short circuit or failure of photocell 25 or of electron tube I50, the switches I and I66 will open. Openin of switch I66 will deenergize holding magnet 85 so that the main burner valve switch 16 will open, Opening of switch I65 will deenergize the main switch holdpilot burner, timing means, means to energize said timing means and said electrically controlled ignition means, pilot burner controlling means operable by said timing means subsequent to operation of said ignition means to render said pilot burner supplying means efiective, means responsive to the occurrence of flame at said pilot burner, means controlled subsequent to the operation of said pilot burner controlling means and by the conjoint action of said timing means and said flame responsive means to render said main burner fuel supplying means effective, means operable by said timing means to stop operation of said pilot burner fuel supplying means, and means instantly operable in response to the occurrence of flame at said main burner to maintain operation of said main burner fuel supplying means upon operation of said last-named means to stop said pilot burner.

4. A fluid fuel burner controlling apparatus comprising a main liquid fuel burner, means to supply liquid'fuel to said burner, means to ignite means to start said liquid fuel supplying means,

and means responsive to occurrence of flame at said burner to maintain operation of said fuel supplying means.

5. A fluid fuel burner controlling apparatus comprising a, main burner havinga liquid fuel supply pipe, an electrically operable valve in said pipe and opened when energized for flow to said burner, an electric heating means for the fuel supplied by said pipe, a thermostatic switch responsive to the temperature of the fuel heated by said heating means and closed upon temperature increase, a timing motor energized by closure of said switch, a fluid fuel pilot burner for igniting said main burner, electric ignition means for said pilot burner and energized by closure of said switch, an electron tube rendered conductive by occurrence of flame at said pilot burner, a relay switch energized by current flow through said tube, an electrically operable valve controlling fiow of fuel to said pilot burner, a switch controlling said pilot burner valve and closed for a short period by said tim-' ing motor, a magnetic holding coil for said pilot burner valve switch, said relay switch when deenergized having closed contacts establishing a circuit through said holding coil, a switch closed by said timing motor to establish a parallel circuit for said holding coil, a pair of switches closed by said timing motor for a short period subsequent to closure of said pilot burner valve switch,

said relay switch having contacts closed upon its 'energization and controlling a circuit for said electrically operable main burner valve in conjunction with one of said last-named timing motor switches, a magnetic holding coil for said last-named pair of timing motor switches, an electron tube rendered conductive by the occurrence of flame at said main burner, a relay switch energized by current flow through said last-named tube and acting in conjunction with the other of said pair of switches to close the circuit (for said last-named holding coil, and means to break the circuit of said last-named holding coil to stop operation of said main burner.

6. In a fluid fuel burner controlling apparatus, a burner, means to supply air and fuel to said burner, a main switch controlling said burner and urged to open position, electrically energizable means to hold said switch closed and energized upon closure of said switch, ignition means for said burner, means responsive to operation of said ignition means and operable to deenergize said energizable holding means, and means to start said ignition means and operable to establish for a predetermined period an alternate circuit to energize said energizable holding means.

'7. In a fluid fuel burner controlling apparatus, a burner, means to supply air and fuel to said burner, a main switch controlling said burner and urged to open position, electrically energizable means to hold said switch closed and energized upon closure of said switch, ignition means for said burner, means responsive to operation of said ignition means and operable to deenergize said energizable holding means, means to start said ignition means and operable to establ s 1: 1 8.

12 predetermined period an alternate circuit to energize said energizable holding means, means responsive to occurrence of flame at said burner, and means operable by said last-named responsive mears to establish another circuit to energize said energizable holding means.

8. In a fluid fuel burner controlling apparatus, a liquid fuel burner, means to supply air and liquid fuel to said burner, a main switch controlling said burner and urged to open position, electrically energizable means to hold said switch closed and energized upon closure of said switch, ignition means for said burner, electric heating means energized by closure of said main switch and operable to heat the liquid fuel, timing means, a thermostatic switch responsive to the temperature of the heated fuel and operable to start said timing means, means operable by said timing means to establish for a predetermined period an alternate circuit to energize said holding means, means operable by said timing means during said period to start said ignition means, means responsive to operation of said ignition means and operable to deenergize said energizable holding means, and means responsive to occurrence of flame at said burner and operable to establish another circuit to energize said energizable holding means to maintain said burner in operation.

9. A fluid fuel burner controlling apparatus, comprising a main burner, electrically operable means to control the supply of fuel to said burner, a pilot burner for igniting said main burner, a solenoid valve controlling the supply of fuel to said pilot burner, electric igniting means for the fuel supplied to said pilot burner, timing means, a switch operable to energize said igniting means and to start said timing means, a pilot burner switch controlling said valve and closed by said timing means, means controlled by said timing means and operable to hold said pilot burner switch closed, cooperable switch means responsive to flame at said pilot burner and to operation-of said timing means and operable to energize said electrically operable main burner supply means, and means responsive to flame at said main burner and operable to maintain energized said main burner supply means.

10. A liquid fuel burner controlling apparatus comprising a main fuel burner, a blower for supplying air to said burner, a. pump for supplying liquid fuel to said burner, a motor for driving said blower and said pump, electric heating means for the fuel supplied by said pump, a gaseous pilot burner for igniting said main burner, an

electric igniter for igniting said pilot burner, a main control switch biased to open position and having a magnetic holding coil, said switch when closed closing the circuit of its holding coil, of said motor and of said heating means, timing means having sequentially operated switches, a thermostatic switch responsive to the temperature of the heated fuel and operable at a predetermined temperature to energize said timing means and said igniter, said timing mean-s acting to close for a predetermined time period one of its switches to establish a holding circuit for itself and an alternate circuit for said igniter and to close another of its switches to establish a holding circuit for said magnetic holding coil, a third timing means switch having a magnetic holding coil maintained energized by closure of said flrst named timing means switch, a, solenoid valve controlling fuel flow to said pilot burner and energized by closure or said third timing means switch,

simultaneously a. main burner controlling switch in parallel circuit with said second-named timing means switch to maintain circuit through the main switch holding coil, a solenoid valve controlled by said 'main burner controlling switch and controlling the discharge from said pump, a fourth one of said timing means switches being closed subsequent to closure of said timing means pilot burner switch and completing a circuit through said last-named solenoid valve from said main burner controlling switch, a magnetic holding coil for said fourth timing means switch, an electron tube rendered conducting in response to flame at said main burner, an electron tube relay energized .by current flow through said lastnamed electron tube, a switch closed by energization of said last-named electron tube relay and cooperating with a flith timing means switch closed upon closure of said fourth timing means switch, said last-named cooperating switches when closed completing a circuit through said last-named magnetic holding coil, said lastnamed electron tube relay when energized closing another switchcooperable with said fifth timing means switch to establish a holding circuit for said main switch holding coil, a safety relay en-' ergized by closure of said fifth timing means switch and closing a holding circuit for its coil in series with said thermostatic switch, and a switch in the starting circuit for said main switch holding coil and opened by said safety relay.

FRED B. AUBERT.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 1,596,836 Hoff Au 1'1, 1926 2,230,732 Tapp et al. Feb. 4, 1941 1,807,376 Braden May 26, 1931 2,306,073 Metcalf Dec. 22, 1942 2,081,091 Kuempel May 18, 1937 2,085,195 Kerr June 29, 1937 1,862,690 Macrae June 14, 1932 2, 8, 51 Brown Nov. 16, 1937 

